1. Field of the Invention
The present invention relates to a vehicular electronic control apparatus for performing, for example, a fuel supply control on an automobile engine and an opening/closing control on an intake throttle valve. In particular, the invention relates to an improved vehicular electronic control apparatus that enables a data-replaced drive at the occurrence of an abnormality in a nonvolatile data memory that cooperates with a microprocessor and to which several kind of variable control data are written.
2. Description of the Related Art
A vehicular electronic control apparatus is known that is provided with a nonvolatile program memory to which control programs, control constants, etc. for a vehicle type to be controlled are written from an external tool, a nonvolatile data memory to which variable control data are written, a RAM for arithmetic processing, and a microprocessor connected to the program memory, the data memory, and the RAM, and that controls vehicular electric loads in accordance with input signals from vehicular sensors and the contents of the program memory and the data memory. In such a vehicular electronic control apparatus, a technique that a nonvolatile data memory such as an EEPROM on which writing can easily performed electrically is utilized as the above-mentioned data memory and various learning data, vehicle-specific data, analysis/maintenance data, etc. are written to the data memory and used as effective drive control data and diagnosis data for an external tool is put in practice use widely.
JP-A-2001-182607 and JP-A-10252547 each entitled “Vehicular Control Apparatus” disclose improved measures against a risk that the power switch may be turned of f accidentally while learning data for correcting control parameters and a control theory by evaluating past control results to eliminate influences of aging variations of a control subject, differences between individual subjects, etc. are being written, for storage, from a RAM to an EEPROM to accommodate a shutoff in the battery lines and an abnormal decrease in the battery voltage.
JP-A-2000-185606 entitled “Vehicular Electronic Control Unit and its Exchange Method” discloses a technique that a VIN code (vehicle-specific data) number is written in advance to a nonvolatile data memory such as an EEPROM, whereby the efficiency of work in exchanging or attaching a vehicular electronic control unit due to occurrence of a problem, for example, is increased.
JP-A-8-121238 entitled “Vehicular Information Storing Apparatus” discloses a means for extracting and storing, every predetermined period, necessary data to write, for storage, long-term analysis/maintenance data to an EEPROM.
JP-A-2000-257502 entitled “Automobile Electronic Control Apparatus,” which is more relevant to the present invention, discloses a technique that the power of an electronic control apparatus is turned off with a delay after a stop of driving of a vehicle (i.e., turning-off of the power switch) and data of a RAM are written divisionally as appropriate to an EEPROM that serves as one or both of a flash memory (program memory) and a data memory while the electronic control apparatus is turned off.
JP-A-2001-227402 entitled “Vehicular Electronic Control Apparatus,” discloses a technique of performing checksum on a program memory while reducing the load of a microprocessor.
Each of the above related art references relates to utilization of a nonvolatile data memory such as an EEPROM and improvement in a method and timing of writing storage data to the data memory in a vehicular electronic control apparatus, and does not refer to how to handle the data stored in the nonvolatile data memory should an abnormality occur in the data.
If the data stored in the nonvolatile data memory are merely past history information and their contents do not influence a present or future drive control, there does not occur any safety-related problem. However, a safety-related problem may arise if control variable data that influence the operation of a microprocessor are stored in the nonvolatile data memory.